//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
const ll mod=998244353;
void upd(ll &a,ll b){a=(a+b)%mod;}
string s;
int n;
ll dp[1001000][2][2][2];
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>s;
	dp[0][0][0][0]=1;
	for(int i=0;i<n;i++)
	{
		for(int a=0;a<2;a++)
			for(int b=0;b<2;b++)
				for(int c=0;c<2;c++)
				{
					upd(dp[i+1][a][b][c],dp[i][a][b][c]);
					for(int x=0;x<2;x++)
						if(s[i]=='?'||(s[i]==x+48))
							upd(dp[i+1][a^1][x][c|(a==0&&b==0&&x==1)],dp[i][a][b][c]);
				}
	}
	ll ans=0;
	for(int b=0;b<2;b++)
		for(int c=0;c<2;c++)
			if(!b||c)
				upd(ans,dp[n][0][b][c]);
	cout<<ans<<endl;
	return 0;
}